pip install fix.

.gitlab-ci.yml

@@ -3,7 +3,7 @@ image: "python:3.6"
 before_script:
   - python --version
   - pip install -U pip
-  - pip install --no-use-pep517 -r requirements.txt
+  - pip install -r requirements.txt --verbose --upgrade --exists-action=i --no-build-isolation
   - pip install -r requirements-dev.txt
 
 stages: